常用的一些占位符：
%@：字符串占位符
%d:整型
%ld:长整型
%f:浮点型
%c:char类型
%%：%的占位符
尽管有那么多的占位符，但是好像没有发现BOOL型的数据的占位符，这也是比较纠结的地方，看了一下别人是怎么解决这个问题的
BOOL studyBool = YES;
NSLog(@"打印BOOL型数据%@",studyBool?@"YES":@"NO");//打印BOOL型数据YES
NSLog(@"打印BOOL型数据%d",studyBool);//打印BOOL型数据1
BOOL alsoBool = NO;
NSLog(@"打印BOOL型数据%@",alsoBool?@"YES":@"NO");//打印BOOL型数据NO
NSLog(@"打印BOOL型数据%d",alsoBool);//打印BOOL型数据0
详细介绍：**********************************************************
%@: Objective-C对象,印有字符串返回descriptionWithLocale:如果于的话,或描述相反.CFTypeRef工作对象,返回的结果的CFCopyDescription功能.(这个翻译有问题建议按照自己的理解方式理解)。
%%: 为'%'字符;
%d,%D,%i: 为32位整型数(int);
%u,%U: 为32位无符号整型数(unsigned int);
%hi: 为有符号的16位整型数(short);
%hu: 为无符号的16位整型数(unsigned shord);
%qi: 为有符号的64位整型数(long long);
%qu: 为无符号的64位整型数(unsigned long long);
%x: 为32位的无符号整型数(unsigned int),打印使用数字0-9的十六进制,小写a-f;
%X: 为32位的无符号整型数(unsigned int),打印使用数字0-9的十六进制,大写A-F;
%qx: 为无符号64位整数(unsigned long long),打印使用数字0-9的十六进制,小写a-f;
%qX: 为无符号64位整数(unsigned long long),打印使用数字0-9的十六进制,大写A-F;
%o,%O: 为32位的无符号整数（unsigned int),打印八进制数;
%f: 为64位的浮点数(double);
%e: 为64位的浮点数(double),打印使用小写字母e,科学计数法介绍了指数的增大而减小;
%E: 为64位的浮点数(double),打印科学符号使用一个大写E介绍指数的增大而减小;
%g: 为64位的浮点数(double),用%e的方式打印指数,如果指数小于4或者大于等于精度,那么%f的风格就会有不同体现;
%G: 为64位的浮点数(double),用%E的方式打印指数,如果指数小于4或者大于等于精度,那么%f的风格就会有不同体现;
%c: 为8位的无符号字符%c(unsigned char),通过打印NSLog()将其作为一个ASCII字符,或者,不是一个ASCII字符,八进制格式\ddd或统一标准的字符编码的十六进制格式\udddd,在这里d是一个数字;
%C: 为16位Unicode字符%C(unichar),通过打印NSLog()将其作为一个ASCII字符,或者,不是一个ASCII字符,八进制格式\ddd或统一标准的字符编码的十六进制格式\\udddd,在这里d是一个数字;
%s: 对于无符号字符数组空终止,%s系统中解释其输入编码,而不是别的,如utf-8;
%S: 空终止一系列的16位Unicode字符;
%p: 空指针(无效*)，打印十六进制的数字0-9和小写a-f,前缀为0x;
%L: 在明确规定的长度下,进行修正,下面的一批数据a,A,e,E,f,F,g,G应用于双精度长整型的参数;
%a: 为64位的浮点数(double),按照科学计数法打印采用0x和一个十六进制数字前使用小写小数点p来介绍指数的增大而减小;
%A: 为64位的浮点数(double),按照科学计数法打印采用0X和一个十六进制数字前使用大写字母小数点P界扫指数的增大而减小；
%F: 为64位的浮点数(double),按照十进制表示法进行打印；
%z: 修改说明在%z长度以下d,i,o,u,x,X适用于某一指定类型的转换或者适用于一定尺寸的整数类型的参数;
%t: 修改说明在%t长度以下d,i,o,u,x,X适用于某一指定类型或一定尺寸的整数类型的转换的参数;
%j: 修改说明在%j长度以下d,i,o,u,x,X适用于某一指定类型或一定尺寸的整数类型的转换的参数。
英文文档
格式定义
The format specifiers supported by the NSString formatting methods and CFString formatting functions follow the IEEE printf specification; the specifiers are summarized in Table 1. Note that you can also use the “n$” positional specifiers such as %1$@ %2$s. For more details, see the IEEE printf specification. You can also use these format specifiers with the NSLog function.
%@ Objective-C object, printed as the string returned by descriptionWithLocale: if available, or description otherwise. Also works with CFTypeRef objects, returning the result of the CFCopyDescription function.
%% ‘%’ character
%d, %D, %i Signed 32-bit integer (int)
%u, %U Unsigned 32-bit integer (unsigned int)
%hi Signed 16-bit integer (short)
%hu Unsigned 16-bit integer (unsigned short)
%qi Signed 64-bit integer (long long)
%qu Unsigned 64-bit integer (unsigned long long)
%x Unsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and lowercase a–f
%X Unsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and uppercase A–F
%qx Unsigned 64-bit integer (unsigned long long), printed in hexadecimal using the digits 0–9 and lowercase a–f
%qX Unsigned 64-bit integer (unsigned long long), printed in hexadecimal using the digits 0–9 and uppercase A–F
%o, %O Unsigned 32-bit integer (unsigned int), printed in octal
%f 64-bit floating-point number (double)
%e 64-bit floating-point number (double), printed in scientific notation using a lowercase e to introduce the exponent
%E 64-bit floating-point number (double), printed in scientific notation using an uppercase E to introduce the exponent
%g 64-bit floating-point number (double), printed in the style of %e if the exponent is less than –4 or greater than or equal to the precision, in the style of %f otherwise
%G 64-bit floating-point number (double), printed in the style of %E if the exponent is less than –4 or greater than or equal to the precision, in the style of %f otherwise
%c 8-bit unsigned character (unsigned char), printed by NSLog() as an ASCII character, or, if not an ASCII character, in the octal format \\ddd or the Unicode hexadecimal format \\udddd, where d is a digit
%C 16-bit Unicode character (unichar), printed by NSLog() as an ASCII character, or, if not an ASCII character, in the octal format \\ddd or the Unicode hexadecimal format \\udddd, where d is a digit
%s Null-terminated array of 8-bit unsigned characters. %s interprets its input in the system encoding rather than, for example, UTF-8.
%S Null-terminated array of 16-bit Unicode characters
%p Void pointer (void *), printed in hexadecimal with the digits 0–9 and lowercase a–f, with a leading 0x
%L Length modifier specifying that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument
%a 64-bit floating-point number (double), printed in scientific notation with a leading 0x and one hexadecimal digit before the decimal point using a lowercase p to introduce the exponent
%A 64-bit floating-point number (double), printed in scientific notation with a leading 0X and one hexadecimal digit before the decimal point using a uppercase P to introduce the exponent
%F 64-bit floating-point number (double), printed in decimal notation
%z Length modifier specifying that a following d, i, o, u, x, or X conversion specifier applies to a size_t or the corresponding signed integer type argument
%t Length modifier specifying that a following d, i, o, u, x, or X conversion specifier applies to a ptrdiff_t or the corresponding unsigned integer type argument
%j Length modifier specifying that a following d, i, o, u, x, or X conversion specifier applies to a intmax_t or uintmax_t argument